The method and system disclosed herein, in general, relates to information communication. More specifically, the method and system disclosed herein relates to communicating multiple channels of distinct data, simultaneously, over the same frequency using multiple linear polarized signals.
Current satellites and ground based radios typically reuse frequencies by transmitting signals in two orthogonal polarities of one of two polarization schemes, namely, left and right hand circular polarization, or vertical and horizontal linear polarization. Normally, no more than two signals can be transmitted along the same or proximate path, each occupying one of two orthogonal polarizations in only one of the two polarization schemes. U.S. Pat. No. 7,590,191 B1, and U.S. Pat. No. 7,957,425 as well as U.S. application Ser. No. 13/237,846 commonly assigned to the applicant have described methods to increase capacity of transmitted electromagnetic signals by using a combination of circularly and linearly polarized signals. There is a need for a method for increasing data carrying capacity using only linearly polarized signals.
In linear polarization, the electric component or the magnetic component of an electromagnetic wave is confined to within a single plane along the direction of propagation of the electromagnetic wave. Linearly polarized signals are either horizontally polarized or vertically polarized, each being orthogonal to the other, that is, rotated 90 degrees around the transmit axis. They do not interfere with each other once transmitted and using polarized receive antennae are received separately without interference from the other.
Polarization of an electromagnetic signal can be established by various methods, for example, through the shape of the radiation elements in the antenna in the case of a lower frequency antenna, or by a dipole feeding into a horn and reflector of a parabolic antenna in a higher frequency band, or by specialized emitters or by filters in the case of light.
A basic principle of electromagnetic waves is the principle of linear superposition: “when two or more waves are present simultaneously at the same place the resultant wave is the sum of the individual waves.” Physics 3rd Edition by Cutnell/Johnson, Wiley and Sons, 1995. ISBN 0-471-59773-2, page 521. “Inverse signals” are two same signals that are exactly 180 degrees out of phase so that when two inverse signals of the same amplitude are combined, they sum to zero power, canceling each other.
As used herein, the term “feed horn” or “feed” refers to an apparatus that includes both a horn and a transducer, also called a polarizer. The transducer may contain a radiator or dipole that emits polarized signals for transmission. A typical transducer is a mechanical device that is attached to the horn. The horn illuminates the antenna, as well as picks up already polarized data signals for reception and passes the received signals on to the transducer. A transducer also routes the data signals from a transmission side of input flanges to the horn or from the horn to a reception side of output flanges.
As used herein, “data signal” refers to an electromagnetic signal modulated to carry information of any kind. “Information signal” and “data signal” both refer to an electromagnetic signal that contains encoded information to be communicated.
A frequency band is a contiguous set of frequencies with a center frequency and multiple side frequencies. Two signals of the “same frequency” means that at least one of the frequencies of the frequency band used to transmit a data signal is the same for both signals, i.e., at least part of the band of frequencies overlaps. Both data signals can occupy the same band or partially overlapping bands. The data signals can convey digital or analog information. The “transmit axis” is the line between a transmitting antenna and a corresponding receive antenna.
Electromagnetic waves do not interact when transmitted through a non absorbing media such as space. Horizontal and vertical linearly polarized data signals do not modify each other once transmitted and pass through space without interference. Until now, due to the noise and interference involved, only two data signals in a single polarization scheme could typically be used to communicate distinct data signals on the same frequency. This means on a given frequency, a maximum of two data signals can be transmitted simultaneously, one on each polarity of the chosen polarization scheme. There is a need for transmitting additional data signals using only linear polarization schemes resulting in increased data carrying capacity. There is a need for a method to transmit up to, for example, three data signals on a same frequency simultaneously by using linear polarized signals.
Hence, there is a long felt but unresolved need for communicating additional distinct data over a single frequency using multiple linearly polarized data signals.